[PATCH] x86_64: Keep only a single debug notifier chain (daeeafec) · Commits · 戴 / test

Calling a notifier three times in the debug handler does not make much sense, because a debugger can figure out the various conditions by itself. Remove the additional calls to DIE_DEBUG and DIE_DEBUGSTEP completely. This matches what i386 does now. This also makes sure interrupts are always still disabled when calling a debugger, which prevents: BUG: using smp_processor_id() in preemptible [00000001] code: tpopf/1470 caller is post_kprobe_handler+0x9/0x70 Call Trace:<ffffffff8024f10f>{smp_processor_id+191} <ffffffff80120e69>{post_kpro be_handler+9} <ffffffff80120f7a>{kprobe_exceptions_notify+58} <ffffffff80144fc0>{notifier_call_chain+32} <ffffffff80110daf>{do_debug+335} <ffffffff8010f513>{debug+127} <EOE> on preemptible debug kernels with kprobes when single stepping in user space. This was probably a bug even on non preempt kernels, this function was supposed to be running with interrupts off according to a comment there. Note to third part debugger maintainers: please double check your debugger can still single step. Cc: <prasanna@in.ibm.com> Cc: <jbeulich@novell.com> Cc: <kaos@sgi.com> Cc: <jim.houston@ccur.com> Cc: <jfv@bluesong.net> Signed-off-by:

Andi Kleen <ak@suse.de> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/traps.c

+3 −11

Original line number	Diff line number	Diff line
		@@ -659,9 +659,9 @@ asmlinkage void do_debug(struct pt_regs * regs, unsigned long error_code)
		asm("movq %%db6,%0" : "=r" (condition));

		if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
		SIGTRAP) == NOTIFY_STOP) {
		SIGTRAP) == NOTIFY_STOP)
		return;
		}

		conditional_sti(regs);

		/* Mask out spurious debug traps due to lazy DR7 setting */
		@@ -674,9 +674,7 @@ asmlinkage void do_debug(struct pt_regs * regs, unsigned long error_code)
		tsk->thread.debugreg6 = condition;

		/* Mask out spurious TF errors due to lazy TF clearing */
		if ((condition & DR_STEP) &&
		(notify_die(DIE_DEBUGSTEP, "debugstep", regs, condition,
		1, SIGTRAP) != NOTIFY_STOP)) {
		if (condition & DR_STEP) {
		/*
		* The TF error should be masked out only if the current
		* process is not traced and if the TRAP flag has been set
		@@ -711,16 +709,10 @@ asmlinkage void do_debug(struct pt_regs * regs, unsigned long error_code)
		force_sig_info(SIGTRAP, &info, tsk);
		clear_dr7:
		asm volatile("movq %0,%%db7"::"r"(0UL));
		notify_die(DIE_DEBUG, "debug", regs, condition, 1, SIGTRAP);
		return;

		clear_TF_reenable:
		set_tsk_thread_flag(tsk, TIF_SINGLESTEP);

		clear_TF:
		/* RED-PEN could cause spurious errors */
		if (notify_die(DIE_DEBUG, "debug2", regs, condition, 1, SIGTRAP)
		!= NOTIFY_STOP)
		regs->eflags &= ~TF_MASK;
		}

include/asm-x86_64/kdebug.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -23,7 +23,6 @@ enum die_val {
		DIE_OOPS = 1,
		DIE_INT3,
		DIE_DEBUG,
		DIE_DEBUGSTEP,
		DIE_PANIC,
		DIE_NMI,
		DIE_DIE,

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